Show custom readme.txt headers in "View Details" dialog

[d4mation]

I'm not sure how extensible this is, but if we could have it show things like "Tested up to LearnDash" that would be super nice.

It currently reads the "Tested up to WordPress" version as that's a part of WP Core. (The proper version is in the develop branch for this plugin, so realbigplugins.com is not reading it yet)

[d4mation]

Note: The custom headers for this are handled via https://github.com/realbigplugins/edd-sl-private-github-readme-custom-headers

[d4mation]

Looking at /wp-admin/plugin-install.php under the install_plugin_information() function, it seems that there is no way to output anything fully custom here :/

We could potentially add a separate Tab to hold this information, but it wouldn't be possible to put it in that right sidebar like the default WP info.

[d4mation]

@BigActual

Thoughts? I'm not sure what we would call an extra tab in this case. Maybe "Additional Information"? All that would go there at this point would be our Custom README Headers, so things like "Tested to LearnDash", "Requires LearnDash", etc.

We could also prepend it to the Description and/or Changelog tabs. This particular view is generally only seen when a user clicks the "View details" link on the Plugin Update screen which defaults to the "Changelog" tab.

[d4mation]

Decision: add this information in a new tab called "Compatibility" or "Compatibility Information"

Will need to decide if this would be best handled within RBP Support (and therefore handled by each of our plugins on the customer's site) or if it'd be best to do so on RBP via https://github.com/realbigplugins/edd-sl-private-github-readme-custom-headers

Currently leaning toward the second one, since then there's "one source of truth" and one outdated plugin of ours on the customer's site wouldn't prevent this code from running.